Modern optical communications networks are universally used to interconnect distant, regional, and metropolitan communications hubs for directing numerous diverse streams of telephony, digital video, internet, and other types of digital data. In order to efficiently and economically manage the ever-increasing capacity and speed demands on these networks, many communications channels are aggregated into streams each carrying up to and foreseeably greater than 100 gigabits per second per aggregated data stream. Dozens of these data streams are transmitted simultaneously through each fiber in the network utilizing dense wavelength-division multiplexing (DWDM) where each stream is carried by an optical signal having an optical wavelength slightly different but fully distinguishable from all the other wavelengths for the other streams in the fiber. The data for each wavelength may be represented as an intensity modulation, typically used for data streams of 10 gigabits per second or below, or the data may be represented by more complex ‘coherent’ modulation of the optical field, which is typically used for data streams carrying greater than 10 gigabits per second. The set of optical data streams that are wavelength multiplexed into an individual fiber may comprise wavelengths that have been modulated according to different data rates and/or different modulation formats. These optical streams are routinely combined and separated as appropriate by various optical filter components at each end of the optical fiber link. Increasingly, it is desirable that the terminal or intermediate optical filtering processes is designed to be insensitive to the embedded optical data rate or format and adaptable to different wavelengths or collections of wavelengths. Herein throughout the use of ‘wavelength’ as a subject refers to a data stream of any appropriate data rate and format encoded onto an optical carrier having a distinctive, but not necessarily herein specified, wavelength. With current communication systems, wavelengths range from about 1250 nanometers (nm) to about 1750 nm, although wavelengths used in communication systems generally evolve with the technology. DWDM systems utilizing optical fiber amplifiers generally use the C-band (approximately 1520 nm to 1570 nm) or L-band (approximately 1570 nm to 1620 nm). Each of these bands spans about 6000 Giga-Hertz (GHz) of optical frequency, and DWDM systems typically segregate these bands into separate channels every 50 GHz or 100 GHz. Even though these channels are allocated and managed according to their optical frequencies, it is customary to call them ‘wavelength’ channels.
The optical networks include many locations where optical fibers intersect and/or provide access points. These locations are commonly referred to as ‘nodes’. Many individual wavelengths come to the node along each of the fibers, but not all the wavelengths on any fiber are necessarily bound for the same destination. Some of the wavelengths may be bound for access destinations local to the node, there may be new wavelengths originating local to the node, and other wavelengths may need to be independently rerouted and re-multiplexed among the various outbound fibers from the node. Management of all these individual wavelengths at the node may be performed in the optical domain or in the electrical domain or distributed into combinations of both. Tradeoffs between optical-domain and electrical-domain switching are many, varied, and application specific. However, in general optical domain switching consumes only a small fraction of the energy that must be provided for electrical-domain switching and also can provide insensitivity to data rates and formats. The power that is provided to the optical node subsystems is substantial and often what limits the available performance and drives the operating costs. It is therefore generally desirable to do as much of the management of wavelengths in the optical domain as is practical.